EXPLANATION OF PLATE TL.— Continued. 



layer cross-shaded. The marginal plates are calcifications of the latter, and 

 the vertebrse of the former. 



a. V. Ambulacral vesicle or ampulla ; F, ambulacral tube foot ; 

 ^.^. genital pore; i?». intermesenteric space; /«c. lacunar spaces in 

 the integument connected with the perihsemal system ; /;, c, pyloric 

 caecum ; r. c. respiratory caecum of perisome ; sp. spine ; n. s., 

 I. s. upper and lower side plates of arm. 



Fig. 4. — Diagrammatic vertical section through an Ophiurid, based upon 

 preparations of Ophioglypha. The right half of the section passes along a 

 ray, and the left half is interradial, 



A^ First ambulacral ossicle (vertebra), or peristomial plate ; 

 A.2...Aq second to sixth ossicles; b.f. buccal feet; c^;. connective- 

 tissue bands, fastening the stomach to the body wall ; 711. lower trans- 

 verse muscle of the second vertebra ; oni'. and mi", external and in- 

 ternal interradial muscles of the oral angle ; m. s. mouth-shield ; 

 0. a. oroangular (interambulacral) piece ; P. polian vesicle ; p. a. palse 

 angulares; S^ — S^ first to sixth under arm plates (superambulacral, 

 Miiller) ; t. a. torus angularis. 



Fig. 5. — Vertical section through the peristome oi AsieracantJdon rubens, 

 close to the middle line of a radius, x 50. 



A-^, A^. First and second ambulacral ossicles ; a, a. Apertures in 

 the vertical septum {v. s.) ; d. connective-tissue membrane above 

 the nerve ; /;. 5. horizontal septum in the perihsemal canal; »i.j and 

 OT.o lower transverse muscles of the first ossicle ; m.^ transverse muscle 

 of the second ossicle ; t. s. and v. s. transverse and vertical septa in 

 the radial perihsemal canal. 



Fig. 6. — Vertical section through the peristome of Asteracanihion rubens, 

 to show the connection of the canalicular spaces of Tiedemann's body {T.) 

 with the water-vascular ring, x 60. 



ep. Thickened epithelium lining the perihsemal ring- canal. 



Fig, 7. — Section through the raadreporic plate of Asterina pentagoiia, 

 near its distal margin. X 45. 



c. Calcareous pieces in integument; m.p. madreporic plate; p. its 

 pores. 



Fig. 8. — Vertical section through the peristome of Asteracanihion rubens, 

 to show the relation of the central plexus and axial perihsemal canal with 

 the oral ring, x 18, 



